Help choosing system for ADT2004

Dear Group:
I am planning to run ADT 2004 on one of two systems. I think both have
limitations and so does my budget right now. Can someone help me with which
one would be better:
Dell Dimension Desktop, P4 2.2gHz, 400mHz front side buss, 768mb (perhaps a
bit more) ram, 40gb HD. The "video card" is called "integrated Intel 3d
extreme graphics" and the available slots for a better card are PCI. It
came with a flat panel 17" monitor. I got a really, really good price.
OR
A machine with dual 450mHz Xeon processors, not sure which video card but I
could get another one, the slots are AGP I think, 1gb ram. This one is free
from a reliable friend, but I would need to buy a flat panel monitor and
possibly a video card.
I understand that the Dell described above has significant speed drawbacks
in 3d, that the 3d circuitry is really not good enough but that the right
card could MOSTLY solve them and that 400mHz front side buss is no longer
the standard but is not too much of a draw back.
The only thing I know about the Xeon based machine is that the processors
will probably not run multithread for ACAD so that I will get 450mHz of
speed, not 900.
Also, I would probably want to run Photoshop and possibly Form Z at the same
time.
Any advice would be most appreciated.
Thanks,
Michael